An OFDM (Orthogonal Frequency Division Multiplexing) modulation method is given as one of digital modulation methods used for wireless communications. In the OFDM modulation method, subcarriers of multicarrier signals are overlapped with each other, resulting in occurrence of high peak power in output signals.
If the peak power of the output signal exceeds a dynamic range of a circuit (e.g., an amplifier and an optical modulator) within an OFDM communication device, a nonlinear distortion occurs in a transmission signal, which might induce deterioration of a transmission characteristic. Such being the case, there is a necessity for designing sufficiently large back-off of a posterior circuit by taking account of Peak to Average Power Ratio (PAPR) of the output signal.
Accordingly, if the PAPR of the output signal becomes too large, the posterior circuit might be upsized, and power efficiency might also be deteriorated. Therefore, a measure for reducing peak amplitude (peak power) of the output signal is taken.
Further, a technology disclosed in, e.g., Patent document 1 given below is exemplified as the prior art related to the invention of the present application.
[Patent document 1]
Japanese Patent Laid-Open Publication No. 2002-271296